Hi there!
I'm battling the bastards as well. DON'T glue them or past any cement or anything onto them. The little devils, will just find another way out. Believe me! Joes Juice, Aptasia X, boiling water, or a banner fish as already mentioned. A Chelmon is a hit or miss issue. I wouldn't get one anymore, sure there habe been successful people keeping them. But I kind of feel sorry for the Chelmons, because they are pretty difficult to keep (and are really beautiful fish!!!). Peppermints are also a hit or miss issue. Just make sure your tank is big enough for a banner, they get big, real big!
Good luck!